Organic light emitting diode display

ABSTRACT

An organic light emitting diode display includes a substrate, a scan line on the substrate for transferring a scan signal, a data line crossing the scan line and for transferring a data signal, a driving voltage line crossing the scan line and for transferring a driving voltage, a switching thin film transistor coupled to the scan line and the data line, a driving thin film transistor coupled to a switching drain electrode of the switching thin film transistor, and an organic light emitting diode (OLED) coupled to a driving drain electrode of the driving thin film transistor, wherein a driving semiconductor layer of the driving thin film transistor is bent and in a plane substantially parallel to the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This continuation application claims priority to U.S. application Ser.No. 13/952,508, filed Jul. 26, 2013, entitled ORGANIC LIGHT EMITTINGDIODE DISPLAY, which claims priority to and the benefit of Korean PatentApplication No. 10-2012-0084976 filed in the Korean IntellectualProperty Office on Aug. 2, 2012, the entire content of which areincorporated herein by reference.

BACKGROUND

1. Field

The described technology relates generally to an organic light emittingdiode display.

2. Description of Related Art

An organic light emitting diode display includes two electrodes and anorganic emission layer interposed therebetween, electrons injected fromone electrode and holes injected from the other electrode are combinedwith each other in the organic emission layer to form an exciton, andlight is emitted while the exciton discharges energy.

The organic light emitting diode display includes a plurality of pixels,each including an organic light emitting diode that is a self-lightemitting element, and a plurality of thin film transistors andcapacitors for driving the organic light emitting diode. The pluralityof thin film transistors includes a switching thin film transistor and adriving thin film transistor.

In the switching thin film transistor, a thin gate insulating layer isformed between a gate electrode and a semiconductor layer to enablerapid switching operation. Because the thickness of the gate insulatinglayer of the driving thin film transistor, which is formed on the samelayer as the switching thin film transistor, is reduced, a driving rangeof a gate voltage applied to the gate electrode of the driving thin filmtransistor becomes narrow. Therefore, it may be difficult to control themagnitude of the gate voltage Vgs of the driving thin film transistor toensure a large number of gray levels.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the describedtechnology, and may therefore contain information that does not form theprior art that is already known in this country to a person of ordinaryskill in the art.

SUMMARY

The described technology provides an organic light emitting diodedisplay broadening a driving range of a driving thin film transistor todisplay a relatively large number of gray levels.

An exemplary embodiment of the present invention provides an organiclight emitting diode display including a substrate, a scan line on thesubstrate for transferring a scan signal, a data line crossing the scanline and for transferring a data signal, a driving voltage line crossingthe scan line and for transferring a driving voltage, a switching thinfilm transistor coupled to the scan line and the data line, a drivingthin film transistor coupled to a switching drain electrode of theswitching thin film transistor, and an organic light emitting diode(OLED) coupled to a driving drain electrode of the driving thin filmtransistor, wherein a driving semiconductor layer of the driving thinfilm transistor is bent and in a plane substantially parallel to thesubstrate.

The organic light emitting diode display may further include a firstgate insulating layer covering the driving semiconductor layer, and astorage capacitor at the first gate insulating layer and overlapping thedriving semiconductor layer.

The storage capacitor may include a first storage capacitor plate at thefirst gate insulating layer and overlapping the driving semiconductorlayer, a second gate insulating layer covering the first storagecapacitor plate, and a second storage capacitor plate at the second gateinsulating layer and overlapping the first storage capacitor plate.

The driving semiconductor layer may include a plurality of bentportions.

The driving semiconductor layer may include a plurality of firstextension portions extending in a first direction, and a plurality ofsecond extension portions extending in a second direction that isdifferent from the first direction, and wherein the bent portions couplerespective ones of the first extension portions and the second extensionportions.

The organic light emitting diode display may further include acompensation thin film transistor coupled to the driving thin filmtransistor and for compensating a threshold voltage of the driving thinfilm transistor.

The driving semiconductor layer may further include branched portionsbranched from the bent portions.

The storage capacitor may overlap the branched portions.

The organic light emitting diode display may further include a lightemission control line for transferring a light emission control signal,and a light emission control thin film transistor configured to beturned on by the light emission control signal to transfer the drivingvoltage from the driving thin film transistor to the OLED, wherein thelight emission control thin film transistor is between the driving drainelectrode and the OLED.

The organic light emitting diode display may further include atransistor connection portion for coupling a compensation sourceelectrode of the compensation thin film transistor to a light emissioncontrol source electrode of the light emission control thin filmtransistor, wherein the storage capacitor extends to overlap thetransistor connection portion.

The driving semiconductor layer may extend to overlap the transistorconnection portion.

The organic light emitting diode display may further include aninterlayer insulating layer on the second gate insulating layer, whereinthe transistor connection portion is at a same layer as the data line,and is coupled through a contact hole in the interlayer insulating layerto the compensation source electrode and the light emission controlsource electrode.

The driving semiconductor layer may include a first path semiconductorlayer coupled to the compensation thin film transistor, and a secondpath semiconductor layer coupled to the light emission control thin filmtransistor, and a length of the first path semiconductor layer may besmaller than a length of the second path semiconductor layer.

The storage capacitor may overlap the first path semiconductor layer andthe second path semiconductor layer.

The organic light emitting diode display may further include aninterlayer insulating layer covering the second storage capacitor plate,a connection member at the interlayer insulating layer and coupled tothe first storage capacitor plate through a first contact hole in thesecond gate insulating layer and the interlayer insulating layer, and aprotective layer covering the interlayer insulating layer and theconnection member, wherein the connection member is coupled to acompensation drain electrode of the compensation thin film transistor.

The scan line is at a same layer as the first storage capacitor plate,and the data line and the driving voltage line may be at a same layer asthe connection member.

The driving voltage line may be coupled through a second contact hole inthe interlayer insulating layer to the second storage capacitor plate.

The organic light emitting diode display may further include anoperation control thin film transistor configured to be turned on by thelight emission control signal transferred by the light emission controlline to transfer the driving voltage to the driving thin filmtransistor, wherein the operation control thin film transistor isbetween the driving voltage line and a driving source electrode of thedriving thin film transistor.

The organic light emitting diode display may further include a priorscan line for transferring a prior scan signal, an initializationvoltage line for transferring an initialization voltage to the drivingthin film transistor, and an initialization thin film transistorconfigured to be turned on according to the prior scan signal totransfer the initialization voltage to a driving gate electrode of thedriving thin film transistor, wherein the initialization thin filmtransistor is between the driving gate electrode and the initializationvoltage line.

The organic light emitting diode display may further include a bypasscontrol line for transferring a bypass control signal, and a bypass thinfilm transistor for transferring a portion of a driving currenttransferred by the driving thin film transistor according to the bypasscontrol signal, wherein the bypass thin film transistor is between theinitialization voltage line and a light emission control drain electrodeof the light emission control thin film transistor.

Another exemplary embodiment of the present invention provides anorganic light emitting diode display including a substrate, a scan lineon the substrate for transferring a scan signal, an initializationvoltage line on the substrate for transferring an initializationvoltage, a data line crossing the scan line for transferring a datasignal, a driving voltage line crossing the scan line for transferring adriving voltage, a switching thin film transistor coupled to the scanline and the data line, a driving thin film transistor coupled to aswitching drain electrode of the switching thin film transistor, anorganic light emitting diode (OLED) coupled to a driving drain electrodeof the driving thin film transistor, a light emission control thin filmtransistor between the driving drain electrode and the OLED, and abypass thin film transistor between the initialization voltage line anda light emission control drain electrode of the light emission controlthin film transistor, wherein the bypass thin film transistor transfersa portion of a driving current transferred by the driving thin filmtransistor according to a bypass control signal transferred by a bypasscontrol line.

A driving semiconductor layer of the driving thin film transistor isbent and in a plane substantially parallel to the substrate.

The organic light emitting diode display may further include a firstgate insulating layer covering the driving semiconductor layer, and astorage capacitor at the first gate insulating layer and overlapping thedriving semiconductor layer.

The storage capacitor may include a first storage capacitor plate at thefirst gate insulating layer and overlapping the driving semiconductorlayer, a second gate insulating layer covering the first storagecapacitor plate, and a second storage capacitor plate at the second gateinsulating layer and overlapping the first storage capacitor plate.

The driving semiconductor layer may include a plurality of bentportions.

The driving semiconductor layer may include a plurality of firstextension portions extending in a first direction, and a plurality ofsecond extension portions extending in a second direction that isdifferent from the first direction. The bent portions may couplerespective ones of the first extension portions and the second extensionportions.

The organic light emitting diode display may further include acompensation thin film transistor coupled to the driving thin filmtransistor and for compensating the threshold voltage of the drivingthin film transistor.

The organic light emitting diode display may further include aninterlayer insulating layer covering the second storage capacitor plate,a connection member at the interlayer insulating layer and coupled tothe first storage capacitor plate through a first contact hole in thesecond gate insulating layer and the interlayer insulating layer, and aprotective layer covering the interlayer insulating layer and theconnection member, The connection member may be coupled to acompensation drain electrode of the compensation thin film transistor.

The scanline may be at a same layer as the first storage capacitorplate, and the data line and the driving voltage line may be at a samelayer as the connection member.

The driving voltage line may be coupled to the second storage capacitorplate through a second contact hole in the interlayer insulating layer.

According to an exemplary embodiment of the present invention, since adriving channel region of a driving semiconductor layer may belongitudinally formed by forming the driving semiconductor layerincluding a plurality of bent portions, a driving range of a gatevoltage applied to a driving gate electrode may be broadened.

Therefore, since the driving range of the gate voltage is relativelybroad, a gray level of light emitted from an organic light emittingdiode (OLED) can be more precisely controlled by adjusting the magnitudeof the gate voltage, and as a result, it is possible to increase aresolution of the organic light emitting diode display and to improvedisplay quality.

Further, it is possible to sufficiently ensure storage capacitance evenat a high resolution by forming a storage capacitor overlapping thedriving semiconductor layer to ensure a region of the storage capacitor,which is reduced by the driving semiconductor layer having the bentportion.

Further, it is possible to avoid or prevent low gray level stains bysetting a length of a first path semiconductor layer coupled to acompensation thin film transistor to be smaller than a length of asecond path semiconductor layer coupled to a light emission control thinfilm transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit of one pixel of an organic lightemitting diode display according to a first exemplary embodiment of thepresent invention.

FIG. 2 is a view schematically showing positions of a plurality of thinfilm transistors and capacitors of the organic light emitting diodedisplay according to the first exemplary embodiment.

FIG. 3 is a layout view of one pixel of the organic light emitting diodedisplay according to the first exemplary embodiment.

FIG. 4 is a cross-sectional view of the organic light emitting diodedisplay of the first exemplary embodiment shown in FIG. 3, which istaken along the line IV-IV.

FIG. 5 is a cross-sectional view of the organic light emitting diodedisplay of the first exemplary embodiment shown in FIG. 3, which istaken along the line V-V.

FIG. 6 is an enlarged layout view of a driving thin film transistor ofan organic light emitting diode display according to a second exemplaryembodiment of the present invention.

FIG. 7 is a layout view of an organic light emitting diode displayaccording to a third exemplary embodiment of the present invention.

FIG. 8 is an enlarged layout view of a driving thin film transistor ofan organic light emitting diode display according to a fourth exemplaryembodiment of the present invention.

FIG. 9 is an enlarged layout view of a driving thin film transistor ofan organic light emitting diode display according to a fifth exemplaryembodiment of the present invention.

FIG. 10 is an equivalent circuit of one pixel of an organic lightemitting diode display according to a sixth exemplary embodiment of thepresent invention.

FIG. 11 is a layout view of the organic light emitting diode displayaccording to the sixth exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described morefully with reference to the accompanying drawings, in which exemplaryembodiments of the invention are shown. As those skilled in the artwould realize, the described embodiments may be modified in variousways, all without departing from the spirit or scope of the presentinvention.

To describe embodiments of the present invention, portions that do notrelate to the description are omitted, and same or like constituentelements are designated by same reference numerals throughout thespecification.

In addition, the size and thickness of each component shown in thedrawings may be arbitrarily shown for understanding and ease ofdescription, but the present invention is not limited thereto. In thedrawings, the thickness of layers, films, panels, regions, areas, etc.,may be exaggerated for clarity, for understanding, and for ease ofdescription. It will be understood that when an element such as a layer,film, region, or substrate is referred to as being “on” another element,it can be directly on the other element, or intervening elements may bepresent.

In addition, unless explicitly described to the contrary, the word“comprise” and variations thereof, such as “comprises” or “comprising”,will be understood to imply the inclusion of stated elements, but notnecessarily to the exclusion of other elements. Further, in thespecification, the word “on” means positioning on or below the objectportion, but does not necessarily mean positioning on the upper side ofthe object portion based on a direction of gravity.

An organic light emitting diode display according to a first exemplaryembodiment will be described in detail with reference to FIGS. 1 to 5.

FIG. 1 is an equivalent circuit of one pixel of an organic lightemitting diode display according to a first exemplary embodiment. Asshown in FIG. 1, one pixel of the organic light emitting diode displayaccording to the first exemplary embodiment includes a plurality ofsignal lines 121, 122, 123, 124, 171, and 172, a plurality of thin filmtransistors T1, T2, T3, T4, T5, and T6, a storage capacitor Cst, and anOLED coupled to the plurality of signal lines.

The plurality of thin film transistors includes a driving thin filmtransistor T1, a switching thin film transistor T2, a compensation thinfilm transistor T3, an initialization thin film transistor T4, anoperation control thin film transistor T5, and a light emission controlthin film transistor T6.

The plurality of signal lines includes a scan line 121 for transferringa scan signal Sn, a prior scan line 122 for transferring a prior scansignal Sn−1 to the initialization thin film transistor T4, a lightemission control line 123 for transferring a light emission controlsignal En to the operation control thin film transistor T5 and the lightemission control thin film transistor T6, a data line 171 crossing thescan line 121 and for transferring a data signal Dm, a driving voltageline 172 for transferring a driving voltage ELVDD and formed to bealmost parallel to the data line 171, and an initialization voltage line124 for transferring an initialization voltage Vint for initializing thedriving thin film transistor T1.

A gate electrode G1 of the driving thin film transistor T1 is coupled toan end Cst1 of the storage capacitor Cst, a source electrode S1 of thedriving thin film transistor T1 is coupled via the operation controlthin film transistor T5 to the driving voltage line 172, a drainelectrode D1 of the driving thin film transistor T1 is electricallycoupled via the light emission control thin film transistor T6 to ananode of the OLED. The driving thin film transistor T1 receives the datasignal Dm according to switching operation of the switching thin filmtransistor T2 to supply a driving current Id to the OLED.

A gate electrode G2 of the switching thin film transistor T2 is coupledto the scan line 121, a source electrode S2 of the switching thin filmtransistor T2 is coupled to the data line 171, a drain electrode D2 ofthe switching thin film transistor T2 is coupled via the operationcontrol thin film transistor T5 to the driving voltage line 172 whilebeing coupled to the source electrode S1 of the driving thin filmtransistor T1. The switching thin film transistor T2 is turned onaccording to the scan signal Sn transferred through the scan line 121 toperform a switching operation for transferring the data signal Dmtransferred to the data line 171 to the source electrode of the drivingthin film transistor T1.

A gate electrode G3 of the compensation thin film transistor T3 iscoupled to the scan line 121, a source electrode S3 of the compensationthin film transistor T3 is coupled via the light emission control thinfilm transistor T6 to the anode of the OLED while being coupled to thedrain electrode D1 of the driving thin film transistor T1, and a drainelectrode D3 of the compensation thin film transistor T3 is coupled toan end Cst1 of the storage capacitor Cst, a drain electrode D4 of theinitialization thin film transistor T4, and the gate electrode G1 of thedriving thin film transistor T1 together. The compensation thin filmtransistor T3 is turned on according to the scan signal Sn transferredthrough the scan line 121 to couple the gate electrode G1 and the drainelectrode D1 of the driving thin film transistor T1 to each other, thusperforming diode-connection of the driving thin film transistor T1.

A gate electrode G4 of the initialization thin film transistor T4 iscoupled to the prior scan line 122, a source electrode S4 of theinitialization thin film transistor T4 is coupled to the initializationvoltage line 124, and a drain electrode D4 of the initialization thinfilm transistor T4 is coupled to the end Cst1 of the storage capacitorCst, the drain electrode D3 of the compensation thin film transistor T3,and the gate electrode G1 of the driving thin film transistor T1. Theinitialization thin film transistor T4 is turned on according to theprior scan signal Sn−1 transferred through the prior scan line 122 totransfer the initialization voltage Vint to the gate electrode G1 of thedriving thin film transistor T1, thus performing an initializationoperation for initializing the voltage of the gate electrode G1 of thedriving thin film transistor T1.

A gate electrode G5 of the operation control thin film transistor T5 iscoupled to the light emission control line 123, a source electrode S5 ofthe operation control thin film transistor T5 is coupled to the drivingvoltage line 172, and a drain electrode D5 of the operation control thinfilm transistor T5 is coupled to the source electrode S1 of the drivingthin film transistor T1 and the drain electrode S2 of the switching thinfilm transistor T2.

A gate electrode G6 of the light emission control thin film transistorT6 is coupled to the light emission control line 123, a source electrodeS6 of the light emission control thin film transistor T6 is coupled tothe drain electrode D1 of the driving thin film transistor T1 and to thesource electrode S3 of the compensation thin film transistor T3, and adrain electrode D6 of the light emission control thin film transistor T6is electrically coupled to the anode of the OLED. The operation controlthin film transistor T5 and the light emission control thin filmtransistor T6 are concurrently (e.g., simultaneously) turned onaccording to the light emission control signal En transferred throughthe light emission control line 123 to transfer the driving voltageELVDD to the OLED, thus allowing a driving current Id to flow in theOLED.

Another end Cst2 of the storage capacitor Cst is coupled to the drivingvoltage line 172, and a cathode of the OLED is coupled to a commonvoltage ELVSS. Accordingly, the OLED receives the driving current Idfrom the driving thin film transistor T1 to emit light, therebydisplaying an image.

Hereinafter, operation of one pixel of the organic light emitting diodedisplay according to the first exemplary embodiment will be described indetail.

First, a prior scan signal Sn−1 of a low level is supplied through theprior scan line 122 during an initialization period. Then, theinitialization thin film transistor T4 is turned on corresponding to theprior scan signal Sn−1 of a low level, and the initialization voltageVint is provided from the initialization voltage line 124 through theinitialization thin film transistor T4 to the gate electrode G1 of thedriving thin film transistor T1 to initialize the driving thin filmtransistor T1 with the initialization voltage Vint.

Subsequently, a low level scan signal Sn is supplied through the scanline 121 during a data programming period. Then, the switching thin filmtransistor T2 and the compensation thin film transistor T3 are turned oncorresponding to a low level scan signal Sn, thereby causing the drivingthin film transistor T1 to be diode-coupled by the turned oncompensation thin film transistor T3, and biased in a forward direction.

Then, a compensation voltage Dm+Vth (Vth is a negative value), which isobtained by subtracting the threshold voltage Vth of the driving thinfilm transistor T1 from the data signal Dm supplied from the data line171, is applied to the gate electrode G1 of the driving thin filmtransistor T1.

The driving voltage ELVDD and the compensation voltage Dm+Vth areapplied to both ends Cst1 and Cst2 of the storage capacitor Cst, and acharge corresponding to a difference between voltages at both ends Cst1and Cst2 is stored in the storage capacitor Cst. Subsequently, the levelof the light emission control signal En supplied from the light emissioncontrol line 123 during the light emission period is changed from a highlevel to a low level. Then, the operation control thin film transistorT5 and the light emission control thin film transistor T6 are turned onby a low level light emission control signal En during the lightemission period.

Then, the driving current Id is generated according to a differencebetween the voltage of the gate electrode G1 of the driving thin filmtransistor T1 and the driving voltage ELVDD, and the driving current Idis supplied through the light emission control thin film transistor T6to the OLED. The gate-source voltage Vgs of the driving thin filmtransistor T1 is maintained at ‘(Dm+Vth)−ELVDD’ by the storage capacitorCst during the light emission period, and the driving current Id isproportional to a square of a difference between the threshold voltageand the source-gate voltage, that is, the driving current Id isproportional to ‘(Dm−ELVDD)²’, according to a current-voltagerelationship of the driving thin film transistor T1. Accordingly, thedriving current Id is determined regardless of the threshold voltage Vthof the driving thin film transistor T1.

A detailed structure of the pixel of the organic light emitting diodedisplay shown in FIG. 1 will be described in detail with reference toFIGS. 2 to 5 together with FIG. 1. FIG. 2 is a view schematicallyshowing positions of the plurality of thin film transistors T1-T6 andthe capacitor Cst elements of the organic light emitting diode displayaccording to the first exemplary embodiment, FIG. 3 is a specific layoutview of one pixel of the organic light emitting diode display accordingto the first exemplary embodiment, FIG. 4 is a cross-sectional view ofthe organic light emitting diode display of the first exemplaryembodiment shown in FIG. 3, which is taken along the line IV-IV, andFIG. 5 is a cross-sectional view of the organic light emitting diodedisplay of the first exemplary embodiment shown in FIG. 3, which istaken along the line V-V.

As shown in FIGS. 2 to 5, the pixel of the organic light emitting diodedisplay according to the first exemplary embodiment includes the scanline 121, the prior scan line 122, the light emission control line 123,and the initialization voltage line 124 formed in a row direction, andfor respectively applying the scan signal Sn, the prior scan signalSn−1, the light emission control signal En, and the initializationvoltage Vint, and also includes the data line 171 and the drivingvoltage line 172 crossing the scan line 121, the prior scan line 122,the light emission control line 123, and the initialization voltage line124, and for respectively applying the data signal Dm and the drivingvoltage ELVDD to the pixel.

Further, in the pixel, the driving thin film transistor T1, theswitching thin film transistor T2, the compensation thin film transistorT3, the initialization thin film transistor T4, the operation controlthin film transistor T5, the light emission control thin film transistorT6, the storage capacitor Cst, and the OLED 70 are formed.

The driving thin film transistor T1, the switching thin film transistorT2, the compensation thin film transistor T3, the initialization thinfilm transistor T4, the operation control thin film transistor T5, andthe light emission control thin film transistor T6 are formed along thesemiconductor layer 131, and the semiconductor layer 131 is bent to havevarious shapes. The semiconductor layer 131 may be formed ofpolysilicon, and includes a channel region, which is not doped with animpurity, and a source region and a drain region formed at respectivesides of the channel region to be doped with the impurity. The type ofimpurity corresponds to the type of thin film transistor, and an N-typeimpurity or a P-type impurity may be used. The semiconductor layer 131includes a driving semiconductor layer 131 a formed in the driving thinfilm transistor T1, a switching semiconductor layer 131 b formed in theswitching thin film transistor T2, a compensation semiconductor layer131 c formed in the compensation thin film transistor T3, aninitialization semiconductor layer 131 d formed in the initializationthin film transistor T4, an operation control semiconductor layer 131 eformed in the operation control thin film transistor T5, and a lightemission control semiconductor layer 131 f formed in the light emissioncontrol thin film transistor T6.

The driving thin film transistor T1 includes the driving semiconductorlayer 131 a, the driving gate electrode 125 a, the driving sourceelectrode 176 a, and the driving drain electrode 177 a. The drivingsemiconductor layer 131 a is bent, and includes a plurality of firstextension portions 31 extending in a first direction, a plurality ofsecond extension portions 32 extending in a second direction that isdifferent from the first direction, and a plurality of bent portions 33coupling respective ones of the first extension portions 31 and thesecond extension portions 32. Accordingly, the driving semiconductorlayer 131 a may be in a zigzag form. The driving semiconductor layer 131a shown in FIGS. 2 and 3 includes three first extension portions 31, twosecond extension portions 32, and four bent portions 33. Accordingly,the driving semiconductor layer 131 a may be longitudinally arranged ina form (e.g., 3 substantially parallel and horizontal lines, wherein thetop and center lines are coupled by a vertical line at one side, andwherein the center and bottom lines are coupled by another vertical lineat an opposite side, as shown in FIG. 6).

As described above, the driving semiconductor layer 131 a may belongitudinally formed in a narrow space by forming the drivingsemiconductor layer 131 a including a plurality of bent portions 33.Accordingly, since the driving channel region 131 a 1 of the drivingsemiconductor layer 131 a may be longitudinally formed, the drivingrange of the gate voltage applied to the driving gate electrode 125 a isbroadened. Therefore, since the driving range of the gate voltage isrelatively broad, a gray level of light emitted from an OLED can be morefinely and precisely controlled by adjusting the magnitude of the gatevoltage, and as a result, it is possible to increase a resolution of theorganic light emitting diode display and improve display quality.

In the driving semiconductor layer 131 a, the first extension portion31, the second extension portion 32, and the bent portion 33 may bevariously located to implement various exemplary embodiments such as‘S’, ‘M’, and ‘W’ (e.g., S-shaped, M-shaped, or W-shaped).

FIG. 6 is an enlarged layout view of a driving thin film transistor ofan organic light emitting diode display according to a second exemplaryembodiment of the present invention.

As shown in FIG. 6, the driving semiconductor layer 131 a may be in theshape of an S.

The driving source electrode 176 a corresponds to the driving sourceregion 176 a doped with the impurity in the driving semiconductor layer131 a, and the driving drain electrode 177 a corresponds to the drivingdrain region 177 a doped with the impurity in the driving semiconductorlayer 131 a. The storage capacitor Cst is formed thereon to overlap thedriving gate electrode 125 a.

The storage capacitor Cst includes a first storage capacitor plate 125 hand a second storage capacitor plate 127 with the second gate insulatinglayer 142 interposed therebetween. Herein, the driving gate electrode125 a also plays a role of the first storage capacitor plate 125 h, thesecond gate insulating layer 142 becomes a dielectric material, andstorage capacitance is determined by the charge accumulated in thestorage capacitor Cst, and by the voltage between both capacitor plates125 a and 127.

The first storage capacitor plate 125 h is separated from the adjacentpixel to form a rectangle, and is formed of the same material as thescan line 121, the prior scan line 122, the light emission control line123, the switching gate electrode 125 b, the compensation gate electrode125 c, the operation control gate electrode 125 e, and the lightemission control gate electrode 125 f, which are on the same layer firststorage capacitor plate 125 h.

The second storage capacitor plate 127 is coupled to the adjacent pixel,and is formed of the same material as the initialization voltage line124, and is formed on the same layer as the initialization voltage line124.

As described above, it is possible to ensure sufficient storagecapacitance even at a high resolution by forming the storage capacitorCst overlapping the driving semiconductor layer 131 a to ensure a regionof the storage capacitor Cst, which is reduced by the drivingsemiconductor layer 131 a having the bent portion.

The switching thin film transistor T2 includes the switchingsemiconductor layer 131 b, the switching gate electrode 125 b, theswitching source electrode 176 b, and the switching drain electrode 177b. The switching source electrode 176 b is a portion protruding from thedata line 171, and the switching drain electrode 177 b corresponds to aswitching drain region 177 b doped with an impurity in the switchingsemiconductor layer 131 b.

The compensation thin film transistor T3 includes the compensationsemiconductor layer 131 c, the compensation gate electrode 125 c, thecompensation source electrode 176 c, and the compensation drainelectrode 177 c. The compensation source electrode 176 c corresponds tothe compensation source region 176 c doped with the impurity in thecompensation semiconductor layer 131 c, and the compensation drainelectrode 177 c corresponds to the compensation drain region 177 c dopedwith the impurity in the compensation semiconductor layer 131 c. Thecompensation gate electrode 125 c prevents a leakage current by forminga separate dual gate electrode 25.

The initialization thin film transistor T4 includes the initializationsemiconductor layer 131 d, the initialization gate electrode 125 d, theinitialization source electrode 176 d, and the initialization drainelectrode 177 d. The initialization drain electrode 177 d corresponds tothe initialization drain region 177 d doped with the impurity in theinitialization semiconductor layer 131 d. The initialization sourceelectrode 176 d is coupled through an initialization connection line 78to the initialization voltage line 124. An end of the initializationconnection line 78 is coupled through a contact hole 161 formed in thesecond gate insulating layer 142 and an interlayer insulating layer 160to the initialization voltage line 124, and another end of theinitialization connection line 78 is coupled through the contact hole162 formed in the gate insulating layer 141, the second gate insulatinglayer 142, and the interlayer insulating layer 160 to the initializationsource electrode 176 d.

The operation control thin film transistor T5 includes the operationcontrol semiconductor layer 131 e, the operation control gate electrode125 e, the operation control source electrode 176 e, and the operationcontrol drain electrode 177 e. The operation control source electrode176 e is a portion of the driving voltage line 172, and the operationcontrol drain electrode 177 e corresponds to the operation control drainregion 177 e doped with the impurity in the operation controlsemiconductor layer 131 e.

The light emission control thin film transistor T6 includes the lightemission control semiconductor layer 131 f, the light emission controlgate electrode 125 f, the light emission control source electrode 176 f,and the light emission control drain electrode 177 f. The light emissioncontrol source electrode 176 f corresponds to the light emission controlsource region 176 f doped with the impurity in the light emissioncontrol semiconductor layer 131 f.

An end of the driving semiconductor layer 131 a of the driving thin filmtransistor T1 is coupled to the switching semiconductor layer 131 b andthe compensation semiconductor layer 131 c, and another end of thedriving semiconductor layer 131 a is coupled to the operation controlsemiconductor layer 131 e and the light emission control semiconductorlayer 131 f. Therefore, the driving source electrode 176 a is coupled tothe switching drain electrode 177 b and to the operation control drainelectrode 177 e, and the driving drain electrode 177 a is coupled to thecompensation source electrode 176 c and to the light emission controlsource electrode 176 f.

The first storage capacitor plate 125 h of the storage capacitor Cst iscoupled through the connection member 174 to the compensation drainelectrode 177 c and to the initialization drain electrode 177 d. Theconnection member 174 is formed on the same layer as the data line 171,an end of the connection member 174 is coupled through a contact hole166 formed in the first gate insulating layer 141, in the second gateinsulating layer 142, and in the interlayer insulating layer 160 to thecompensation drain electrode 177 c and to the initialization drainelectrode 177 d, and another end of the connection member 174 is coupledthrough a contact hole 167 formed in the second gate insulating layer142 and in the interlayer insulating layer 160 to the first storagecapacitor plate 125 h. In this case, another end of the connectionmember 174 is coupled through a storage opening 27 formed in the secondstorage capacitor plate 127 to the first storage capacitor plate 125 h.

The second storage capacitor plate 127 of the storage capacitor Cst iscoupled through a contact hole 168 formed in the interlayer insulatinglayer 160 to a driving voltage line 172.

The switching thin film transistor T2 is used as a switching element forselecting the pixel that is to emit light. The switching gate electrode125 b is coupled to the scan line 121, the switching source electrode176 b is coupled to the data line 171, and the switching drain electrode177 b is coupled to the driving thin film transistor T1 and to theoperation control thin film transistor T5. In addition, the lightemission control drain electrode 177 f of the light emission controlthin film transistor T6 is directly coupled through a contact hole 181formed in the protective layer 180 to a pixel electrode 191 of anorganic light emitting diode 70.

Hereinafter, referring to FIGS. 4 and 5, a structure of the organiclight emitting diode display according to the first exemplary embodimentwill be described in detail according to the lamination order.

The structure of the thin film transistor will be described based on thedriving thin film transistor T1, the switching thin film transistor T2,and the light emission control thin film transistor T6. In addition, thelaminate structures of the film transistors T3, T4, and T5 are almostthe same as the laminate structures of the driving thin film transistorT1, the switching thin film transistor T2, and the light emissioncontrol thin film transistor T6, and thus, the remaining thin filmtransistors T3, T4, and T5 are not described in further detail.

A buffer layer 111 is formed on the substrate 110, and the substrate 110may be formed of an insulating substrate made of glass, quartz,ceramics, plastics or the like.

The driving semiconductor layer 131 a, the switching semiconductor layer131 b, and the light emission control semiconductor layer 131 f areformed on the buffer layer 111. The driving semiconductor layer 131 aincludes a driving source region 176 a and a driving drain region 177 afacing each other with a driving channel region 131 a 1 interposedtherebetween, the switching semiconductor layer 131 b includes aswitching source region 132 b and a switching drain region 177 b facingeach other with a switching channel region 131 b 1 interposedtherebetween, and the light emission control thin film transistor T6includes a light emission control channel region 131 f 1, the lightemission control source region 176 f, and the light emission controldrain region 133 f.

Since the driving semiconductor layer 131 a includes a plurality of bentportions 33 to be formed in a zigzag form, specifically, in a ‘

’ form, the driving semiconductor layer 131 a may be longitudinallyformed in a narrow space. Accordingly, since the driving channel region131 a 1 of the driving semiconductor layer 131 a may be longitudinallyformed, the driving range of the gate voltage applied to the drivinggate electrode 125 a may be broadened.

The first gate insulating layer 141 formed of silicon nitride (SiNx) orsilicon oxide (SiO2) is formed on the switching semiconductor layer 131a, the driving semiconductor layer 131 b, and the light emission controlsemiconductor layer 131 f.

The first gate wires including the scan line 121, which includes thedriving gate electrode 125 a, the switching gate electrode 125 b, andthe compensation gate electrode 125 c, the prior scan line 122, whichincludes the initialization gate electrode 125 d, and the light emissioncontrol line 123, which includes the operation control gate electrode125 e and the light emission control gate electrode 125 f, are formed onthe first gate insulating layer 141.

The driving gate electrode 125 a is separated from the scan line 121,and the floating gate electrode 25 overlaps the driving channel region131 a 1 of the driving semiconductor layer 131 a. In addition, theswitching gate electrode 125 b is coupled to the scan line 121, and theswitching gate electrode 125 b overlaps the switching channel region 131b 1 of the switching semiconductor layer 131 b. In addition, the lightemission control gate electrode 125 f overlaps the light emissioncontrol channel region 131 f 1 of the light emission controlsemiconductor layer 131 f.

Because, in the switching thin film transistor T2, only the first gateinsulating layer 141 is formed between the switching gate electrode 125b and the switching semiconductor layer 131 b, it is possible to performa relatively rapid switching operation, and in the driving thin filmtransistor T1, only the first gate insulating layer 141 is formedbetween the driving gate electrode 125 a and the driving semiconductorlayer 131 a, but since the length of the driving channel region 131 a 1of the driving semiconductor layer 131 a is relatively large, thedriving range of the gate voltage applied to the driving gate electrode125 a is relatively broadened, such that it is possible to more finely,or precisely, control the gray level of light emitted from the OLED.

The first gate wires 125 a, 125 b, 125 c, 125 d, 125 e, 125 f, 121, 122,and 123 and the first gate insulating layer 141 cover the second gateinsulating layer 142. The second gate insulating layer 142 may be formedof silicon nitride (SiNx) or silicon oxide (SiO2).

Second gate wires including the second storage capacitor plate 127 andthe initialization voltage line 124 are formed on the second gateinsulating layer 142. The second storage capacitor plate 127 overlapsthe first storage capacitor plate 125 h to form the storage capacitorCst, and the first storage capacitor plate 125 h overlaps the drivingsemiconductor layer 131 a. As described above, it is possible to ensurethe storage capacitance, even at a high resolution wherein the size ofthe pixel is reduced, by ensuring a region of the storage capacitor Cstreduced by the driving semiconductor layer 131 a having the bent portion33 by forming the storage capacitor Cst overlapping the drivingsemiconductor layer 131 a.

The interlayer insulating layer 160 is formed on the second gateinsulating layer 142, on the second storage capacitor plate 127, and onthe initialization voltage line 124. The first gate insulating layer141, the second gate insulating layer 142, and the interlayer insulatinglayer 160 together have a contact hole 163 through which the lightemission control drain region 133 f of the light emission controlsemiconductor layer 131 f is exposed. Like the first gate insulatinglayer 141 and the second gate insulating layer 142, the interlayerinsulating layer 160 may be made of a ceramic-based material such assilicon nitride (SiNx) or silicon oxide (SiO2).

Data wires including the data line 171, the switching source electrode176 b, the driving voltage line 172, the connection member 174, and thelight emission control drain electrode 177 f, are formed on theinterlayer insulating layer 160.

In addition, the switching source electrode 176 b and the light emissioncontrol drain electrode 177 f are coupled through the contact holes 164and 163 formed in the interlayer insulating layer 160, in the first gateinsulating layer 141, and in the second gate insulating layer 142 to theswitching source region 132 b of the switching semiconductor layer 131 band to the light emission control drain region 133 f of the lightemission control semiconductor layer 131 f, respectively.

The protective layer 180, which covers the data wires 171, 172, 174, and177 f, is formed on the interlayer insulating layer 160, and the pixelelectrode 191 is formed on the protective layer 180. The pixel electrode191 is coupled through the contact hole 181 formed in the protectivelayer 180 to the light emission control drain electrode 177 f.

A barrier rib 350 is formed on an edge of the pixel electrode 191 andthe protective layer 180, and the barrier rib 350 has a barrier ribopening 351 through which the pixel electrode 191 is exposed. Thebarrier rib 350 may be made of, for example, resins such aspolyacrylates and polyimides or silica-based inorganic materials.

An organic emission layer 370 is formed on the pixel electrode 191exposed through the barrier rib opening 351, and the common electrode270 is formed on the organic emission layer 370. As described above, theorganic light emitting diode 70 including the pixel electrode 191, theorganic emission layer 370, and the common electrode 270 is formed.

Herein, the pixel electrode 191 is an anode that is a hole injectionelectrode, and the common electrode 270 is a cathode that is an electroninjection electrode. However, the present invention is not limitedthereto, and the pixel electrode 191 may be the cathode, and the commonelectrode 270 may be the anode, according to the driving method of theorganic light emitting diode display. Holes and electrons arerespectively injected from the pixel electrode 191 and the commonelectrode 270 into the organic emission layer 370, and when the exciton,which results from the combined injected holes and electrons, falls froman excited state to a bottom state, light is emitted.

The organic emission layer 370 may be formed of a low molecular weightorganic material, or a high molecular weight organic material such as,for example, PEDOT (poly 3,4-ethylenedioxythiophene). Further, theorganic emission layer 370 may be formed of a multilayer structureincluding one or more of an emission layer, a hole injection layer HIL,a hole transport layer HTL, an electron transport layer ETL, and anelectron injection layer EIL. In the case where all the layers areincluded, the hole injection layer HIL is located on the pixel electrode710, which is the anode, and the hole transport layer HTL, the emissionlayer, the electron transport layer ETL, and the electron injectionlayer EIL are sequentially laminated thereon. Since the common electrode270 is formed of a reflective conductive material, a rear surface lightemission-type organic light emitting diode display is realized. Materialsuch as lithium (Li), calcium (Ca), lithium fluoride/calcium (LiF/Ca),lithium fluoride/aluminum (LiF/Al), aluminum (Al), silver (Ag),magnesium (Mg), or gold (Au) may be used as the reflective material.

In the first exemplary embodiment, the first storage capacitor plate 125h has a rectangular shape. However, a third exemplary embodiment of thepresent invention enables increased storage capacitance by extending aportion of the first storage capacitor plate 125 h.

Referring now to FIG. 7, an organic light emitting diode displayaccording to the third exemplary embodiment of the present inventionwill be described in detail, wherein FIG. 7 is a layout view of anorganic light emitting diode display according to a third exemplaryembodiment.

The third exemplary embodiment of the present invention is substantiallythe same as the first exemplary embodiment shown in FIGS. 1 to 5, withthe exception of the driving semiconductor layer and the storagecapacitor, and thus a repeated description of the similar features willbe omitted.

As shown in FIG. 7, the driving thin film transistor T1 of the organiclight emitting diode display according to the third exemplary embodimentincludes the driving semiconductor layer 131 a, the driving gateelectrode 125 a, the driving source electrode 176 a, and the drivingdrain electrode 177 a. The driving semiconductor layer 131 a is bent,and includes a plurality of first extension portions 31 extending in afirst direction, a plurality of second extension portions 32 extendingin a second direction that is different from the first direction, and aplurality of bent portions 33 coupling respective ones of the firstextension portions 31 and the second extension portions 32.

The driving semiconductor layer 131 a may extend from a lateral surfaceof the data line 171 to be adjacent to the data line 171. Accordingly,since the length of the driving semiconductor layer 131 a is increased,the driving range of the gate voltage applied to the driving gateelectrode 125 a may be broadened.

In the third exemplary embodiment, the compensation source electrode 176c of the compensation thin film transistor T3, and the light emissioncontrol source electrode 176 f of the light emission control thin filmtransistor T6, are formed on the same layer, but the compensation sourceelectrode 176 c and the light emission control source electrode 176 fare separated from each other with a spacing portion d therebetween soas to not overlap the driving semiconductor layer 131 a.

The driving gate electrode 125 a, that is, the first storage capacitorplate 125 h may extend in a lateral direction to overlap the extendeddriving semiconductor layer 131 a, and the first storage capacitor plate125 h may partially overlap the spacing portion d. In addition, thesecond storage capacitor plate 127 extends so as to overlap the firststorage capacitor plate 125 h, and the second storage capacitor plate127 partially overlaps the spacing portion d.

The compensation source electrode 176 c and the light emission controlsource electrode 176 f, which are partially separated from each other,are coupled to each other through the transistor connection portion 71formed on the same layer as the data line 171. An end of the transistorconnection portion 71 is coupled through a contact hole 61 formed in thefirst gate insulating layer 141, in the second gate insulating layer142, and in the interlayer insulating layer 160, to the compensationsource electrode 176 c. Another end of the transistor connection portion71 is coupled through a contact hole 62 formed in the first gateinsulating layer 141, in the second gate insulating layer 142, and inthe interlayer insulating layer 160, to the light emission controlsource electrode 176 f. Accordingly, the storage capacitor Cst extendsto overlap the transistor connection portion 71, and the drivingsemiconductor layer 131 a extends to overlap the transistor connectionportion 71.

As described above, since the compensation source electrode 176 c andthe light emission control source electrode 176 f may be coupled throughthe transistor connection portion 71 to allow the driving semiconductorlayer 131 a, the first storage capacitor plate 125 h, and the secondstorage capacitor plate 127 to extend to the spacing portion d betweenthe compensation source electrode 176 c and the light emission controlsource electrode 176 f, the storage capacitor Cst may be furtherextended.

In the first exemplary embodiment, the driving semiconductor layer 131 ais not directly coupled to the compensation source electrode 176 c atthe bent portion 33. However, in a fourth exemplary embodiment of thepresent invention, a branched portion 34 is directly branched from thecompensation source electrode 176 c at the bent portion 33.

Now referring to FIG. 8, an organic light emitting diode displayaccording to the fourth exemplary embodiment will be described indetail. FIG. 8 is an enlarged layout view of a driving thin filmtransistor of an organic light emitting diode display according to thefourth exemplary embodiment. The fourth exemplary embodiment issubstantially the same as the first exemplary embodiment shown in FIGS.1 to 5, with the exception of the driving semiconductor layer and thestorage capacitor, and thus, repeated description of the substantiallysimilar features will be omitted.

As shown in FIG. 8, the driving thin film transistor T1 of the organiclight emitting diode display according to the fourth exemplaryembodiment includes the driving semiconductor layer 131 a, the drivinggate electrode 125 a, the driving source electrode 176 a, and thedriving drain electrode 177 a. The driving semiconductor layer 131 a isbent, and includes the first extension portion 31 extending in a firstdirection, the second extension portion 32 extending in a seconddirection that is different from the first direction, the bent portion33 coupling the first extension portion 31 and the second extensionportion 32, and the branched portion 34 directly branched to thecompensation source electrode 176 c at the bent portion 33. The entiredriving semiconductor layer 131 a has a ‘┤’ form (e.g., a vertical linehaving a horizontal line extending from near a center of the verticalline). Accordingly, since the length of the driving semiconductor layer131 a is increased, the driving range of the gate voltage applied to thedriving gate electrode 125 a may be broadened.

The branched portion 34 corresponds to a first path semiconductor layerCH1 coupled to the compensation thin film transistor T3, and the secondextension portion 32 corresponds to a second path semiconductor layerCH2 coupled to the light emission control thin film transistor T6. Inaddition, the driving gate electrode 125 a, that is, the first storagecapacitor plate 125 h, overlaps the first path semiconductor layer CH1and the second path semiconductor layer CH2 of the driving semiconductorlayer 131 a, and the second storage capacitor plate 127 overlaps thefirst storage capacitor plate 125 h. Accordingly, since the area of thestorage capacitor Cst is increased, sufficient storage capacitance canbe attained even at a high resolution.

In the fourth exemplary embodiment, the lengths of the first pathsemiconductor layer CH1 and the second path semiconductor layer CH2 aresubstantially the same as each other. However, in a fifth exemplaryembodiment of the present invention, the lengths of the first pathsemiconductor layer CH1 and the second path semiconductor layer CH2 aredifferent from each other.

Referring now to FIG. 9, an organic light emitting diode displayaccording to the fifth exemplary embodiment of the present embodimentwill be described in detail. FIG. 9 is an enlarged layout view of adriving thin film transistor of an organic light emitting diode displayaccording to the fifth exemplary embodiment, which is substantially thesame as the fourth exemplary embodiment shown in FIG. 8, with theexception of the driving semiconductor layer and the storage capacitor,and thus a repeated description of the similarities will be omitted.

As shown in FIG. 9, the driving thin film transistor T1 of the organiclight emitting diode display according to the fifth exemplary embodimentincludes the driving semiconductor layer 131 a, the driving gateelectrode 125 a, the driving source electrode 176 a, and the drivingdrain electrode 177 a. The driving semiconductor layer 131 a is bent.The driving semiconductor layer 131 a includes the first extensionportion 31 extending in a first direction, the second extension portion32 extending in a second direction that is different from the firstdirection, the bent portion 33 coupling the first extension portion 31and the second extension portion 32, and the branched portion 34directly branched from the compensation source electrode 176 c at thebent portion 33. Accordingly, since the length of the drivingsemiconductor layer 131 a is increased, the driving range of the gatevoltage applied to the driving gate electrode 125 a may be broadened.

The branched portion 34 corresponds to the first path semiconductorlayer CH1 coupled to the compensation thin film transistor T3, and azigzag portion 30, which includes the first extension portion 31, thesecond extension portion 32, and the bent portion 33, corresponds to thesecond path semiconductor layer CH2 coupled to the light emissioncontrol thin film transistor T6. In addition, the driving gate electrode125 a, that is, the first storage capacitor plate 125 h, overlaps thefirst path semiconductor layer CH1 and the second path semiconductorlayer CH2 of the driving semiconductor layer 131 a, and the secondstorage capacitor plate 127 overlaps the first storage capacitor plate125 h. Accordingly, since the area of the storage capacitor Cst isincreased, sufficient storage capacitance can be ensured even at a highresolution.

Further, the length of the first path semiconductor layer CH1 is smallerthan the length of the second path semiconductor layer CH2. Thisstructure is called a short pass diode structure, and since the lengthof the first path semiconductor layer CH1 is different from the lengthof the second path semiconductor layer CH2, currents having differentmagnitudes may concurrently (e.g., simultaneously) flow. Since thelength of the first path semiconductor layer CH1 is relatively small, arelatively large current may flow therein, and since the length of thesecond path semiconductor layer CH2 is relatively large, relativelysmall currents may flow therein (e.g., at a same time as the relativelylarge current in the first path semiconductor layer CH1). As describedabove, a constant current may be provided to the organic light emittingdiode while a threshold voltage is rapidly compensated by using acharacteristic of concurrently (e.g., simultaneously) providing currentshaving different magnitudes by one driving thin film transistor toreduce a current variation between the driving thin film transistorshaving different characteristics, thus preventing stains caused by adifference between magnitudes of the currents, and the driving operationthereof will be described in detail below.

The driving thin film transistor T1 charges the voltage corresponding tothe data signal Dm in the storage capacitor Cst according to the scansignal Sn, and provides the current corresponding to the voltage chargedin the storage capacitor Cst to the OLED. Because the threshold voltageVth of the driving thin film transistor T1 may be changed over time, thecompensation thin film transistor T3 performs diode-connection of thedriving thin film transistor T1 according to the scan signal Sn tocompensate the threshold voltage Vth of the driving thin film transistorT1.

Accordingly, since the relatively large current flowing through thefirst path semiconductor layer CH1 while the data signal Dm istransferred can rapidly charge the storage capacitor Cst through thecompensation thin film transistor T3 (e.g., to a predeterminedvoltage/compensation voltage), the compensation of the threshold voltageVth may be relatively rapidly and easily performed.

Further, the relatively small current flowing through the second pathsemiconductor layer CH2 is provided through the light emission controlthin film transistor T6 to the OLED, stains may be avoided or prevented.That is, since a change in current according to a change in voltageapplied to the driving gate electrode 125 a of the driving thin filmtransistor T1 is small, a current control voltage width (data swingrange) can be increased, such that the range of the data voltagedisplaying a gamma can be increased, and it is possible to avoid orprevent stains caused by a difference between magnitudes of the currentsby reducing a current variation between the driving thin filmtransistors having different characteristics (e.g., distributioncharacteristics).

Since a known driving thin film transistor can allow only a current ofone magnitude to flow through the driving semiconductor layer 131 a,currents having the same magnitude are provided to the compensation thinfilm transistor T3 and the light emission control thin film transistorT6. Accordingly, when the length of the driving semiconductor layer 131a of the driving thin film transistor T1 is relatively small, so thatthe threshold voltage Vth of the driving thin film transistor T1 israpidly compensated, because an s-factor of a transistor characteristiccurve (transfer curve) is reduced, thereby increasing a ratio (e.g.,change ratio) of a change in current to a change in voltage applied tothe driving gate electrode, thereby causing a relatively large currentto be provided to the OLED, potentially causing stains.

Conversely, when the length of the driving semiconductor layer 131 a ofthe driving thin film transistor T1 is set to be relatively large in anattempt to avoid or prevent stains, because the threshold voltage Vth ofthe driving thin film transistor is compensated by the small currentrelatively slowly, low gray level compensation is not performed, causingstains. This problem becomes more noticeable as the resolution isincreased. That is, because an amount of time during which the datasignal Dm is applied is reduced as the resolution is increased, thecurrent flows to the OLED before the threshold voltage Vth is completelycompensated, causing the current variation to generate stains.

Accordingly, it is possible to avoid or prevent low gray level stains bysetting the length of the first path semiconductor layer CH1 coupled tothe compensation thin film transistor T3 to be smaller than the lengthof the second path semiconductor layer CH2 coupled to the light emissioncontrol thin film transistor T6.

The first exemplary embodiment has a structure where the drivingsemiconductor layer of the driving thin film transistor is bent in a“6tr 1cap” structure, which is formed of six thin film transistors andone storage capacitor. However, a sixth exemplary embodiment of thepresent embodiment has a structure where the driving semiconductor layerof the driving thin film transistor is bent in a “7tr 1cap” structureformed of seven thin film transistors and one storage capacitor.

Referring now to FIGS. 10 and 11, an organic light emitting diodedisplay according to the sixth exemplary embodiment will be described indetail. FIG. 10 is an equivalent circuit of one pixel of an organiclight emitting diode display according to the sixth exemplaryembodiment, and FIG. 11 is a layout view of the organic light emittingdiode display according to the sixth exemplary embodiment, which issubstantially the same as the first exemplary embodiment shown in FIGS.1 to 5, except that a current control thin film transistor is added, andthus a repeated description of similarities will be omitted.

As shown in FIGS. 10 and 11, one pixel of the organic light emittingdiode display according to the sixth exemplary embodiment includes aplurality of signal lines 121, 122, 123, 124, 128, 171, and 172, and aplurality of thin film transistors T1, T2, T3, T4, T5, T6, and T7, thestorage capacitor Cst, and the OLED coupled to a plurality of signallines.

The plurality of thin film transistors includes the driving thin filmtransistor T1, the switching thin film transistor T2, the compensationthin film transistor T3, the initialization thin film transistor T4, theoperation control thin film transistor T5, the light emission controlthin film transistor T6, and the current control thin film transistorT7.

The signal line includes the scan line 121 for transferring the scansignal Sn, the prior scan line 122 for transferring the prior scansignal Sn−1 to the initialization thin film transistor T4, the lightemission control line 123 for transferring the light emission controlsignal En to the operation control thin film transistor T5 and to thelight emission control thin film transistor T6, the data line 171crossing the scan line 121 and for transferring the data signal Dm, thedriving voltage line 172, which is substantially parallel to the dataline 171, for transferring the driving voltage ELVDD, the initializationvoltage line 124 for transferring the initialization voltage Vint forinitializing the driving thin film transistor T1, and a bypass controlline 128 for transferring a bypass signal BP to a bypass thin filmtransistor T7.

The gate electrode G1 of the driving thin film transistor T1 is coupledto an end (e.g., a first end) Cst1 of the storage capacitor Cst, thesource electrode S1 of the driving thin film transistor T1 is coupledvia the operation control thin film transistor T5 to the driving voltageline 172, the drain electrode D1 of the driving thin film transistor T1is electrically coupled via the light emission control thin filmtransistor T6 to an anode of the OLED.

The gate electrode G2 of the switching thin film transistor T2 iscoupled to the scan line 121, the source electrode S2 of the switchingthin film transistor T2 is coupled to the data line 171, the drainelectrode D2 of the switching thin film transistor T2 is coupled via theoperation control thin film transistor T5 to the driving voltage line172, while also being coupled to the source electrode S1 of the drivingthin film transistor T1.

The gate electrode G4 of the initialization thin film transistor T4 iscoupled to the prior scan line 122, the source electrode S4 of theinitialization thin film transistor T4 is coupled to the initializationvoltage line 124, and the drain electrode D4 of the initialization thinfilm transistor T4 is coupled to the first end Cst1 of the storagecapacitor Cst, to the drain electrode D3 of the compensation thin filmtransistor T3, and to the gate electrode G1 of the driving thin filmtransistor T1.

A gate electrode G7 of the bypass thin film transistor T7 is coupled tothe bypass control line 128, a source electrode S7 of the bypass thinfilm transistor T7 is coupled to the drain electrode D6 of the lightemission control thin film transistor T6 and to the anode of the OLED,and a drain electrode D7 of the bypass thin film transistor T7 iscoupled to the initialization voltage line 124 and to the sourceelectrode S4 of the initialization thin film transistor T4.

Hereinafter, operation of the bypass thin film transistor T7 of theorganic light emitting diode display according to the sixth exemplaryembodiment will be described.

The bypass thin film transistor T7 receives the bypass signal BP fromthe bypass control line 128. The bypass signal BP is a voltage (e.g., avoltage of a predetermined level) at which the bypass thin filmtransistor T7 can be always turned off, and the bypass thin filmtransistor T7 receives the voltage of a level sufficient to turn thetransistor off to the gate electrode G7 to turn off the bypasstransistor T7, and allow a portion of the driving current Id to flow asa bypass current Ibp through the bypass transistor T7.

When the minimum current of the driving thin film transistor T1 fordisplaying a black image flows as the driving current Id, if the OLEDemits light, the black image is not ideally displayed. Accordingly, thebypass thin film transistor T7 of the organic light emitting diodedisplay according to the sixth exemplary embodiment may disperse, ordivert, a portion of the minimum current of the driving thin filmtransistor T1 as a bypass current Ibp to a current path other than thecurrent path of the organic light emitting diode. Herein, the minimumcurrent of the driving thin film transistor refers to a current when thegate-source voltage Vgs of the driving thin film transistor T1 issmaller than the threshold voltage Vth, thus turning off the drivingthin film transistor. The minimum driving current (e.g., current of 10pA or less) when the driving thin film transistor is turned off istransferred to the organic light emitting diode to be displayed as animage of black luminance.

When the minimum driving current displaying the black image flows, abypass transferring effect of the bypass current Ibp is large, but whenthe large driving current for displaying an image (such as a generalimage or a white image) flows, an effect of the bypass current Ibp ishardly present. Accordingly, when the driving current displaying theblack image flows, a light emitting current Ioled of the organic lightemitting diode, which corresponds to the driving current Id reduced bythe bypass current Ibp through the bypass thin film transistor T7, hasthe minimum required current at which the black image can be displayed.

Accordingly, a contrast ratio may be improved by implementing a preciseblack luminance image by using the bypass thin film transistor T7.

A structure of the pixel of the organic light emitting diode displayshown in FIG. 10 will be described with reference to FIG. 11 togetherwith FIGS. 10 and 3. FIG. 11 is a layout view of the organic lightemitting diode display according to the sixth exemplary embodiment.

As shown in FIGS. 10 and 11, the pixel of the organic light emittingdiode display according to the sixth exemplary embodiment includes thescan line 121, the prior scan line 122, the light emission control line123, the initialization voltage line 124, and the bypass control line128 formed in a row direction for respectively applying the scan signalSn, the prior scan signal Sn−1, the light emission control signal En,the initialization voltage Vint, and the bypass signal BP, and alsoincludes the data line 171 and the driving voltage line 172 crossing thescan line 121, the prior scan line 122, the light emission control line123, the initialization voltage line 124, and the bypass control line128, and for respectively applying the data signal Dm and the drivingvoltage ELVDD to the pixel.

Further, in the pixel, the driving thin film transistor T1, theswitching thin film transistor T2, the compensation thin film transistorT3, the initialization thin film transistor T4, the operation controlthin film transistor T5, the light emission control thin film transistorT6, the bypass thin film transistor T7, the storage capacitor Cst, andthe OLED 70 are formed.

The driving thin film transistor T1, the switching thin film transistorT2, the compensation thin film transistor T3, the initialization thinfilm transistor T4, the operation control thin film transistor T5, thelight emission control thin film transistor T6, and the bypass thin filmtransistor T7 are formed along the semiconductor layer 131, which isbent to have various shapes. The semiconductor layer 131 may be formedof, for example, polysilicon, and includes a channel region not dopedwith an impurity, and a source region and a drain region formed atrespective sides of the channel region and doped with an impurity.Herein, the impurity corresponds to a kind of thin film transistor, suchas, for example, an N-type impurity or a P-type impurity. Thesemiconductor layer 131 includes the driving semiconductor layer 131 aformed in the driving thin film transistor T1, the switchingsemiconductor layer 131 b formed in the switching thin film transistorT2, the compensation semiconductor layer 131 c formed in thecompensation thin film transistor T3, the initialization semiconductorlayer 131 d formed in the initialization thin film transistor T4, theoperation control semiconductor layer 131 e formed in the operationcontrol thin film transistor T5, the light emission controlsemiconductor layer 131 f formed in the light emission control thin filmtransistor T6, and a bypass semiconductor layer 131 g formed in thebypass thin film transistor T7.

The driving thin film transistor T1 includes the driving semiconductorlayer 131 a, the driving gate electrode 125 a, the driving sourceelectrode 176 a, and the driving drain electrode 177 a. The drivingsemiconductor layer 131 a is bent, and includes a plurality of firstextension portions 31 extending in a first direction, a plurality ofsecond extension portions 32 extending in a second direction that isdifferent from the first direction, and a plurality of bent portions 33coupling respective ones of the first extension portions 31 and thesecond extension portions 32. Accordingly, the driving semiconductorlayer 131 a may be in a zigzag form. The driving semiconductor layer 131a shown in FIGS. 2 and 3 includes three first extension portions 31, twosecond extension portions 32, and four bent portions 33. Accordingly,the driving semiconductor layer 131 a may be longitudinally in a form,or in a z form.

As described above, the driving semiconductor layer 131 a may belongitudinally formed in a narrow space by forming the drivingsemiconductor layer 131 a including a plurality of bent portions 33.Accordingly, since the driving channel region 131 a 1 of the drivingsemiconductor layer 131 a may be longitudinally formed, the drivingrange of the gate voltage applied to the driving gate electrode 125 a isbroadened. Therefore, since the driving range of the gate voltage isrelatively broad, a gray level of light emitted from an OLED can be morefinely, or precisely, controlled by changing or adjusting the magnitudeof the gate voltage, and as a result, it is possible to increase aresolution of the organic light emitting diode display and to improvedisplay quality.

The bypass thin film transistor T7 includes the bypass semiconductorlayer 131 g, the bypass gate electrode 125 g, the bypass sourceelectrode 176 g, and the bypass drain electrode 177 g. The bypass sourceelectrode 176 g corresponds to the bypass drain region 177 g doped withthe impurity in the bypass semiconductor layer 131 g, and the bypassdrain electrode 177 g corresponds to the bypass drain region 177 g dopedwith the impurity in the bypass semiconductor layer 131 g. The bypasssource electrode 176 g is directly coupled to the light emission controldrain region 133 f.

The bypass semiconductor layer 131 g is formed on the same layer as thedriving semiconductor layer 131 a, the switching semiconductor layer 131b, the light emission control semiconductor layer 131 f, and the like.The first gate insulating layer 141 is formed on the bypasssemiconductor layer 131 g. The bypass gate electrode 125 g, which is aportion of the bypass control line 128, is formed on the first gateinsulating layer 141, and the second gate insulating layer 142 is formedon the bypass gate electrode 125 g and the first gate insulating layer141.

Accordingly, the bypass thin film transistor T7 receives the bypasssignal BP from the bypass control line 128 to always turn off the bypasstransistor T7, and a portion of the driving current Id is emitted underan off state as the bypass current Ibp through the bypass transistor T7to the outside. Accordingly, when the driving current displaying theblack image flows, a contrast ratio may be improved by implementing amore precise black luminance image.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, and their equivalents.

Description of Some of the Reference Characters 31: First extensionportion 32: Second extension portion 33: Bent portion 110: Substrate121: Scan line 122: Prior scan line 123: Light emission control line124: Initialization voltage line 125a: Driving gate electrode 125b:Switching gate electrode 131a: Driving semiconductor layer 132b:Switching semiconductor layer 141: First gate insulating layer 142:Second gate insulating layer 171: Data line 172: Driving voltage line

What is claimed is:
 1. An organic light emitting diode displaycomprising: a substrate; a scan line on the substrate for transferring ascan signal; a data line crossing the scan line and for transferring adata signal; a driving voltage line crossing the scan line and fortransferring a driving voltage; a switching thin film transistor coupledto the scan line and the data line; a driving thin film transistorcoupled to a switching drain electrode of the switching thin filmtransistor, and comprising a driving semiconductor layer and a drivinggate electrode; a first insulating layer covering the drivingsemiconductor layer; an organic light emitting diode (OLED) coupled to adriving drain electrode of the driving thin film transistor; and astorage capacitor on the first insulating layer having a plurality ofstorage capacitor plates, wherein at least one of the storage capacitorplates comprises the driving gate electrode.
 2. The organic lightemitting diode display of claim 1, wherein the storage capacitorcomprises: a first storage capacitor plate on the first insulatinglayer; a second insulating layer covering the first storage capacitorplate; and a second storage capacitor plate on the second insulatinglayer and overlapping the first storage capacitor plate, and wherein thefirst storage capacitor plate comprises the driving gate electrode. 3.The organic light emitting diode display of claim 2, wherein the firststorage capacitor plate is the same plate as the driving gate electrode.4. The organic light emitting diode display of claim 2, wherein thesecond storage capacitor plate overlaps the first storage capacitorplate in a plan view.
 5. The organic light emitting diode display ofclaim 1, wherein the storage capacitor overlaps the drivingsemiconductor layer.
 6. The organic light emitting diode display ofclaim 1, wherein the driving semiconductor layer is bent in a plan view.7. The organic light emitting diode display of claim 6, wherein thedriving semiconductor layer comprises a plurality of bent portions. 8.The organic light emitting diode display of claim 6, wherein the drivingsemiconductor layer has an S-shape or a reversed S-shape in a plan view.9. The organic light emitting diode display of claim 6, wherein thedriving semiconductor layer has an M-shape or a reversed M-shape in aplan view.
 10. The organic light emitting diode display of claim 9,wherein the storage capacitor overlaps the driving semiconductor layerin a plan view.
 11. The organic light emitting diode display of claim 6,wherein the organic light emitting diode comprises a first electrodecoupled to the driving drain electrode, and wherein the first electrodeoverlaps the driving semiconductor layer in a plan view.